The present invention relates to an optical modulator module, and particularly to the optical modulator module to be used for a transmitter for optical communications.
An optical modulator module has been required to be downsized. JP-A-2003-318601 provides an optical module having a bended transmission line, in which good frequency characteristics can be obtained when being driven at a high frequency, so as to obtain a degree of freedom of the internal arrangement for realization of a high-density package.
A chip carrier 24, a high frequency substrate 29, and a lens 22 are mounted in a package 28 as shown in FIG. 6 in JP-A-2003-318601. An EA-DFB (Electro-Absorption Modulator Integrated Distributed Feedback) laser diode 21 is mounted on the chip carrier 24. The EA-DFB laser diode 21 is optically coupled to an optical fiber 23 via the lens 22. The chip carrier 24 and the high frequency substrate 29 have a chip carrier transmission line 25 and a high frequency substrate transmission line 27, respectively, which are connected to each other via a wire 31. In addition, a package substrate also has a package substrate transmission line 26 which is connected to the high frequency substrate transmission line 27 via a wire 32. A photodiode mounted on a photodiode mount is generally disposed at the rear (opposite to the fiber) of the chip carrier 24.
In the optical modulator module disclosed in JP-A-2003-318601, in the case where the chip carrier transmission line 25 and the package substrate transmission line 26 are not linearly-arranged, the high frequency substrate transmission line 27 is bent without deteriorating the frequency characteristics so as to realize a high-density package while obtaining a good optical output waveform.
US 2003/0202800 A1 is the U.S. counterpart application of JP-A-2003-318601.
In order to downsize the optical modulator module, the reduction in dimension of components while securing a degree of freedom of the arrangement is of importance. There has been a problem in that the more the dimension of components is reduced, the more the inductance components of a wire are increased due to the following reason. In the case where the width of a signal transmission line is 200 μm or more, there is provided means by which the inductance of a wire is decreased by connecting the transmission lines via a ribbon wire or plural wires. However, in the case where the substrate is made thinner and the width of the transmission line is reduced for the sake of further downsizing, it is difficult to use the ribbon wire as well as to arrange the plural wires, which results in no choice but to connect the transmission lines via one wire. Consequently, the inductance components are increased to cause reduction in transmission band of the transmission line, and as a result, the optical output waveform of the optical modulator module is distorted.
In order to solve the problem, it is effective to reduce a distance of the wire connection by improving the dimension accuracy of components and the assembly accuracy of components. However, this improvement causes a sharp rise in cost of components.